1. Field of the Invention
The present invention relates to techniques for improving transmission of audio signals over a digital network and particularly to improving audio clarity and intelligibility at reduced bit rates over a digital network.
2. Description of the Prior Art
The growth of the Internet is doubling every 18 months, with over 57 million Domain hosts as of July 1999. In the United States, 42% of the population has Internet access. The use of audio transmitted over the Internet is growing even faster. According to iRadio (February 1999), 13% of all Americans have listened to radio on the world wide web, which is up from 6% only half a year before. However, the delivery of audio over the Internet is limited by low bit rate connections. The present invention enhances the quality of audio (Music or Voice) for transmission over a digital network, such as the Internet, before it is transmitted over the network. This invention enhances audio delivered separately or as part of a video download or video stream.
Audio that is broadcast over the Internet in real-time is called streaming audio. Radio stations, concerts, speeches and lectures are all delivered over the web in streaming form. Encoders such as those offered by Microsoft and Real Audio reside on servers that deliver the audio stream at multiple bit rates over various connections (modem, T1, DSL, ISDN etc.) to the listener's computer. Upon receipt, the streamed data is decoded by a “player” that understands the particular encoding format.
FIG. 1 shows the basic transport path of audio over the network. The Audio Server 10 sends digital audio files through a connection such as a T1 line 12 to a digital network 18 such as the Internet using a defined protocol such as Transport Control Protocol/Internet Protocol (TCP/IP). From the network 18 the listener can connect his client computer 15 to the network 18 using a point-to-point (POP) connection 14. As the audio files enter the client computer they can be listened through the speakers 16.
To improve audio clarity and intelligibility it is desirable to equalize the amplitude of sound and music over time intervals as well as across the entire frequency spectrum. In particular, when music or voice becomes louder and softer and most of the high volume sound is concentrated in a narrow frequency band the need to equalize the sound amplitude over different frequencies becomes greater.
At present, there are radio broadcasting systems such as Orban and other music production systems capable of equalizing voice and music in real-time and over a range of frequencies. However, such systems generally require a sophisticated operator and powerful hardware for implementation, which makes them both labor-intensive and expensive. Due to its enhanced quality, transmission of processed audio at lower bit rates can have more clarity and presence than transmission of non-processed audio at higher bit rates. The result is an increase in bandwidth availability in a given network.
Therefore, the need arises for a method and apparatus for improving audio transmission across any digital network, such as the Internet, in real-time and by enhancing audio quality and intelligibility at reduced bit rates.